The Idea of an Essay, Volume 2

125 was experimentally determined by Mitchell and Skinner (2009) that the giraffe’s heart mass depends on the size of the giraffe. They dissected fifty-six giraffe hearts, weighed them, and compared the weight to the mass of the giraffe. They concluded that the heart’s size is proportional to the weight of the giraffe. In the ten giraffe fetuses that they dissected, they found that the heart was larger than the body mass, but this is usually the case among all mammals (Mitchell & Skinner, 2009; Holt et al, 1968). Since the size of the giraffe’s heart is not surprisingly big in proportion to its body, how does it supply the brain with the oxygen- and nutrient-rich blood it needs? In order for the heart to pump the blood up the carotid artery to the brain, the heart must be strong enough and be able to overcome the hydrostatic, or pressure due to gravity (Zhang, 2006). However, the size of the heart does not determine its strength. Instead, it is the structure of the heart that determines its strength (Mitchell & Skinner, 2009). According to Mitchell and Skinner (2009), they found, experimentally, that the structure of the heart is determined by the neck length. The further the brain is away from the heart, the higher the blood pressure, thus the magnitude of hypertension in giraffes is dependent on the neck length (Mitchell & Skinner, 2009). The high blood pressure affects the thickness of the walls of the left ventricle of the heart. (Mitchell & Skinner, 2009). Therefore, the longer the neck, the more hypertrophy, or thickening, occurs in the left ventricle. The left ventricle is the lower left chamber in the heart that pumps blood to the entire body. Without the thickening and strengthening of this ventricle, the heart would not be able to pump a sufficient amount of blood to the brain or body of the giraffe (Mitchel & Skinner, 2009). The hypertrophy of this ventricle occurs because the ventricle must work exceptionally hard in order to pump the blood up the carotid artery to the brain of the giraffe. As the giraffe grows, the neck becomes longer and hypertrophy of the left ventricle increases. The graph below demonstrates this relationship between the neck length and the left ventricle wall thickness, where “LVWT” represents the left ventricle and the “IVWT” stands for interventricular wall thickness which is irrelevant to this study.